Electrodeposition, among other processes, is used as a manufacturing technique for the application of films (e.g., metal films) to various structures and surfaces, such as semiconductor wafers and silicon workpieces. An important feature of systems used for such processes is their ability to produce films with uniform and repeatable characteristics such as film thickness, composition, and profile relative to the underlying workpiece profile.
A number of factors can prevent the formation of a uniform film. For example, the plating current can spread out when passing from the anode to the cathode of the system, which can result in thicker plated deposits near the outer edge of a workpiece. In addition, the fluid distribution in a process chamber, particularly at an anode or cathode surface, may not be uniform. Non-uniform fluid distribution at the cathode can cause a variation in the thickness of the diffusion boundary layer across the workpiece surface, which can lead to non-uniform film thickness. Moreover, inefficient fluid mixing near a surface where a film is being deposited can result in air or gas bubbles becoming entrapped at the surface. This can inhibit further deposition in the vicinity of the gas bubble, which can cause a non-uniform deposition. Finally, if a workpiece is not securely retained in a process chamber, the position of the workpiece can change during processing, and when fluid processing a workpiece, fluid can leak into unwanted areas if a secure, fluid-tight seal is not formed with the workpiece.
Prior art systems suffer from one or more of these limitations, and a need therefore exists for new and improved methods and apparatus for controlling fluid flow and electric field distribution during the fluid processing of a workpiece and for reliably retaining a workpiece during processing.